The usual and most optimum place for a single p/up is two or three inches from the bridge, so you're quite right to pop one in there. The reason is that a steel guitar can be played way higher than you normally would on a regular guitar and, because the tone changes when the bar gets nearer the p/up, we put it as far as possible from the fret-board end. How far away from the bridge is the p/up you've fitted? Your description suggests it's quite a way off the bridge and that may even rob you of some upper fret-board.
String spacing should be what suits you best. Many lap steel guitars have wider spacing than (for instance) Fender 8string consoles and PSGs; it can make picking and slants easier. Yours may have to be spaced to match the pickup.
Here's a "seven" I made a while ago, the bridge is just below the front of the hand-rest and the middle of the p/up is about 2.5in from it. String spacing was dictated simply by the width of the wood I had for the neck

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PS - Keith and I are mates and we have quite a bit of experience in making (and playing) these things, usually made out of "available" materials, please feel free to PM if you think either of us can be of any help
